In recent years, mobile radio equipment has been used to communicate not only by voice but also with images as multimedia progresses, and performs additional functions such as high-speed data transmission, Internet access and the like. It is desirable for the implementation of such functions that the mobile radio equipment be comprised of two independent functional blocks for carrying out a transmission system function and an application function, respectively. Accordingly, a lower layer serves the transmission system function for mainly exchanging a communication protocol with base stations, while an upper layer has the application function for providing user interface and executing application software.
In the following, the configuration of conventional mobile radio equipment will be described.
FIG. 1 is a block diagram showing the configuration of conventional mobile radio equipment.
As can be seen in FIG. 1, the mobile radio equipment comprises an antenna 1, a radio transmitter/receiver 2, a transmission system function CPU 3, an application function CPU 4, a decoder 5, an input/output section 6 and a memory 7.
The radio transmitter-receiver 2 transmits/receives data or radio signals via the antenna 1 according to the mobile communication system of the mobile radio equipment. When the mobile radio equipment adopts, for example, W-CDMA (Wideband Code Division Multiple Access), the radio transmitter-receiver includes a separator-coupler, an oscillator, a PLL (Phase Locked Loop), a modulator-demodulator, a spreader- reverse spreader for processing baseband signals, and a rake receiver.
The transmission system function CPU 3 controls the radio transmitter-receiver 2, and converts or customizes the data received by the transmitter-receiver 2 to a data format acceptable to the application function CPU 4.
The application function CPU 4 decodes the data input from the transmission system function CPU 3, and executes application software. In addition, the application function CPU 4 controls the input/output section 6 and the memory 7.
The decoder 5 decodes received data using a decoding system compliant with the mobile communication system of the mobile radio equipment and the format of the received data. There are a variety of encoding/decoding systems for multimedia communication data, such as 3G-324M, H. 263, MPEG-4, and MPEG-2.
The input/output section 6 serves as the external interface of the mobile radio equipment. The input/output section 6 includes, for example, communication units such as a microphone and a speaker, a display unit such as an LCD, and an input unit such as a CCD camera. Additionally, the input/output section 6 may include a data communication interface USB (Universal Serial Bus), IEEE1394, Bluetooth and the like.
The memory 7 stores data handled by the application function CPU 4. Examples of the memory 7 include a ROM, a RAM, an IC card, a memory card, a memory card with copyright protection and a disk storage.
When establishing communication, the mobile radio equipment informs a radio base station of the maximum transmission rate at which it can receive data from the base station. Subsequently, the radio base station adjusts resources to allocate resources to the mobile radio equipment newly connected thereto. After that, the radio base station determines the transmission rate for the mobile radio equipment, and enters into communication with the radio equipment.
There is found an example of the conventional technique in Japanese Patent Application laid open No. 2000-92023. In the radio communication system of the conventional technique, a radio line is operated at a data transfer rate or communication rate which can be selected from predetermined values regardless of whether or not communication has already been established. A radio communication terminal changes the communication rate in response to a request from a radio base station. The radio base station informs a correspondent terminal as to the change of the communication rate.
There is found another example of the conventional technique in Japanese Patent Application laid open No. 2002-171572. The conventional technique aims at preventing a packet loss due to the difference of data transfer rate between a terrestrial network and a radio section in a mobile communication system, and also making most efficient use of the transmission performance of radio channels.
Besides, Japanese Patent Application laid open No. HEI10-243048 discloses a system and method for information transmission enabling effective data transmission based on the processing performance of each information communication terminal. With the system and method for information transmission, it is possible to prevent needless transmission as well as the needless use of a disk on the terminal side, and clear contents can be displayed according to the display performance of each terminal.
However, in the above-described conventional techniques, the resources of the radio base station are limited, and maximum efficiency cannot be achieved. Moreover, although the mobile radio equipment demands the maximum rate of data transmission, it does not have a decoding capability commensurate with the maximum transmission rate even if its radio transmission function is sufficient to receive data normally.